Your are getting the error because you are linking in your cricket_i1_v00.cpp (I am guessing this is where your main is located), you are including the input.cpp and in your project you probably have input.cpp as one of source file to your project. So, you are compiling the source "input.cpp" twice in essence. This is why Infinity08 is suggesting that you create an .h file. The basic convention is that declarations get placed in a .h file and object definitions get placed in the .cpp file.

There is no magic to the #include statement. You might as cut and pasted the code at the point where the #include is.